Andersson S A, Holmgren E
Am J Chin Med (Gard City N Y). 1975 Oct;3(4):311-34. doi: 10.1142/s0192415x75000396.
The effect on the experimental tooth pain threshold of conditioning electrical stimulation via needles or surface electrodes applied to the hands and cheeks was studied in 34 dental students. Conditioning stimulation with 2/sec. gave a slowly increasing pain threshold followed by a slow return to the control level in the post-conditioning period. In each individual the amplitude of the threshold increase was reproduceable. It was concluded that these effects are not due to motivational but to more basic neurophysiological mechanisms. The pain threshold was increased mainly by segmental conditioning stimulation; segmentally unrelated stimulation gave usually only small effects. Conditioning stimulation with 100/sec. produced only a strict segmental short-lasting effect. Effects with characteristics of both 2/sec. and 100/sec. were obtained by conditioning at 10/sec. It is suggested that the transmission of impulses from the pain afferents to ascending pathways is controlled at the segmental level by (a) presynaptic inhibition within the group of afferents giving rise to the flexion reflex of which the pain afferents are assumed to be a part; (b) postsynaptic inhibition between alternate pathway excited by flexion reflex afferents; and (c) descending control from supraspinal systems which may utilize similar segmental mechanisms as the primary afferents.
在34名牙科学生中研究了通过针电极或表面电极对手部和脸颊施加条件电刺激对实验性牙齿疼痛阈值的影响。以2次/秒的频率进行条件刺激时，疼痛阈值会缓慢升高，随后在条件刺激后阶段缓慢恢复到对照水平。在每个个体中，阈值升高的幅度都是可重复的。得出的结论是，这些效应不是由于动机因素，而是由于更基本的神经生理机制。疼痛阈值的升高主要是由节段性条件刺激引起的；与节段无关的刺激通常只会产生很小的影响。以100次/秒的频率进行条件刺激时，仅产生严格的节段性短期效应。以10次/秒的频率进行条件刺激时，可获得兼具2次/秒和100次/秒刺激特征的效应。有人提出，痛觉传入神经向上升通路的冲动传递在节段水平上受以下因素控制：(a) 在假定痛觉传入神经是其一部分的、引发屈肌反射的传入神经组内的突触前抑制；(b) 由屈肌反射传入神经兴奋的交替通路之间的突触后抑制；以及(c) 脊髓上系统的下行控制，其可能利用与初级传入神经类似的节段机制。
